1. Field of the Invention
The present invention relates to a fixing apparatus including a fixing member, a pressure member that forms a nip portion with the fixing member to apply pressure to a recording material, and an external heating portion that forms a nip portion through contact with the fixing member, and that has an external heating belt capable of externally heating the fixing member.
2. Description of the Related Art
There has conventionally been known a fixing apparatus having a fixing roller and a pressure roller, wherein the fixing roller includes a heat-generating member incorporated therein. In the configuration in which the heat-generating member is incorporated in the fixing roller, the thermal conductivity of a metal core or an elastic layer of the fixing roller is low, so that heat on the surface of the fixing roller is absorbed to allow the temperature on the surface of the fixing roller to be easy to be reduced during the time when the recording material passes between the fixing roller and the pressure roller. The quantity of heat required for a recording material (thick paper) to fix an image and having a great grammage is greater than the quantity of heat required for a recording material (thin paper) having a small grammage to fix an image, so that, when the recording material (thick paper) having a great grammage passes between the fixing roller and the pressure roller, the temperature on the surface of the fixing roller tends to be reduced. Therefore, toner is defectively fixed on the recording material, which might cause a deterioration in the image quality.
Japanese Patent Application Laid-Open No. 2009-069220 discloses a fixing apparatus as an invention for suppressing the temperature drop on the surface of the fixing roller described above. The fixing apparatus described in Japanese Patent Application Laid-Open No. 2009-069220 includes a fixing roller, a pressure roller, a heating belt of an endless belt type that abuts against the surface of the fixing roller, and a heating roller around which a pressure belt is looped, and that has a halogen lamp incorporated therein. According to this configuration, the heat of the halogen lamp is propagated to the heating roller, the heating belt, and the fixing roller, whereby the temperature drop on the surface of the fixing roller is prevented.
The fixing apparatus described in Japanese Patent Application Laid-Open No. 2009-069220 includes a heating and canceling mechanism that allows the heating belt to be in contact with the fixing roller so as to be capable of heating the heating belt, and that allows the heating belt to be separated from the fixing roller so as to stopl the heating. When the fixing roller has a temperature not less than a predetermined temperature during a warm-up period, the heating belt abuts against the fixing roller. After a power source of a main body of the apparatus is turned off, the heating belt is separated from the fixing roller. With this configuration, a curl formed on the heating belt is corrected, so that the defective rotation of the heating belt is prevented, whereby the defective fixing is prevented to suppress the deterioration in image quality.
However, in the mechanism described in Japanese Patent Application Laid-Open No. 2009-069220, the heat is propagated to the fixing roller from the heating belt immediately before the recording material passes between the fixing roller and the pressure roller, and a problem arises when the heating belt is changed to a contact state in which the heating belt is in contact with the fixing roller from a separated state in which the heating belt is separated from the fixing roller. This problem will be described with reference to FIG. 9.
FIG. 9 is a sectional view illustrating a configuration of a fixing apparatus 300 having a heating and canceling mechanism 350 described in Japanese Patent Application Laid-Open No. 2009-069220. As illustrated in FIG. 9, in the fixing apparatus 300, a fore part of a heating belt 383 is brought into contact with a rotating fixing roller 360, but two rollers 381 and 382 are not abutted thereagainst during the change from the separated state to the contact state.
In the state in which the fore part of the heating belt 383 is in contact with the fixing roller 360, but the two rollers 381 and 382 are not abutted against the fixing roller 360 as described above, the heating belt 383 is not driven with the fixing roller 360, whereby the heating belt 383 and the fixing roller 360 are in sliding friction with each other. With the sliding friction, sliding-friction damage is produced on the surface of the heating belt 383 and the surface of the fixing roller 360. This sliding-friction damage can cause a deterioration of toner gloss (glaze), and toner or powders of the recording material can suffer sliding-friction damage, which might cause a deterioration in the image quality. Further, once the sliding-friction damage occurs, it is easy for the toner and powders of the recording material to acculumulate the sliding-friction damage, with the result that damage, which appears on an image, might be formed on the surface of the fixing roller at an accelerated rate.
The present invention aims to provide a fixing apparatus that can reduce a sliding friction between an external heating belt and a fixing member.